Adhesion and Detachment Mechanisms between Polymer
and Solid Substrate Surfaces: Using Polystyrene–Mica as a Model
System

The adhesion and
detachment of polymer and solid substrate surfaces
play important roles in many engineering applications such as for
designing adhesives, biomedical adhesives, adhesive tapes, robust
protective coatings, biomedical scaffolds, prosthetic devices (e.g.,
artificial joints and implants), and fabrication of micro- and nanoelectromechanical
devices. In this work, a surface forces apparatus (SFA) coupled with
top-view optical microscopy was employed to measure the adhesion between
thin polystyrene (PS) films and a mica substrate to probe their detachment
behaviors. Various factors, including molecular weight (MW), contact
time, and polarity-enhancing UV/ozone treatment, were examined. The
results show that increased chain-end density, chain mobility, and
segment polarity can all contribute to enhanced adhesion strength
for both the “symmetric” PS–PS and “asymmetric”
PS–mica systems but attributed to different adhesion/detachment
mechanisms. For the <i>asymmetric</i> PS–mica system,
the increased chain-end density (lower MW), increased chain mobility,
and increased polarity (induced by UV/ozone treatment) facilitate
the rearrangement of the polystyrene chains and the development of
mainly “polar” interactions such as dipole–dipole,
dipole–induced dipole, and attractive hydrogen bond interactions
between the polar groups on the UV-treated PS (the π-electron
clouds of the phenyl rings) and the highly polar mica surface. For
the <i>symmetric</i> PS–PS system, the enhanced adhesion
is mainly due to the interdiffusion, interdigitation, interpenetration,
and entanglement of chains across the polymer–polymer contact
interface. Importantly, during the separation of a UV/ozone-treated
PS surface from mica, “stick–slip” detachment
was observed, resulting in a residue of concentric polymer rings left
on the mica surface. Our results provide new fundamental and practical
insights into the adhesion, detachment, and damage (wear) mechanisms
of polymer–polymer and polymer–solid surfaces.